Method and a device for maintaining or replacing a tether line

Abstract

The invention relates to a method for maintaining or replacing a tether line ( 22 ) anchoring a buoyancy unit to an underwater or seabed anchoring installation, characterized in that a pull down line ( 12,12 a, 12 b″ ) is connected to the buoyancy unit and the line is guided through a block ( 21 ) fixed to the lower anchoring installation, and then the buoyancy unit is pulled down to slacken the tether line ( 22 ), and the sufficient maintenance or replacement is performed. A device is also disclosed.

The invention claimed is: 
     
       1. A method for maintaining or replacing a tether line that is anchoring a buoyancy unit to an underwater or seabed anchoring installation, comprising the steps: connecting a pull down line to the buoyancy unit; guiding the pull down line through a block fixed to a lower anchoring installation; pulling down the buoyancy unit to slacken the tether line; and then performing maintenance or replacement on the tether line. 
     
     
       2. The method according to  claim 1 , further comprising: installing and operating the pull down line by a winch arrangement of an installation vessel. 
     
     
       3. The method according to  claim 2 , further comprising: using a block unit including a pulley unit. 
     
     
       4. The method according to  claim 3 , further comprising: connecting the block unit to pre-installed shackles adjacent a sea bed anchoring unit; and connecting the pull down line to pre-installed shackles adjacent the buoyancy unit. 
     
     
       5. The method according to  claim 1 , further comprising: connecting a tether line upper termination to the buoyancy unit via a ROV operable interface component. 
     
     
       6. The method according to  claim 1 , further comprising: connecting a tether line lower termination to a seabed anchoring unit via a ROV operable interface component; and connecting a padeye unit to the seabed anchor. 
     
     
       7. The method according to  claim 1 , further comprising: installing the pull down line by means of a ROV. 
     
     
       8. Device for maintaining or replacing a tether line anchoring a buoyancy unit to an underwater or seabed anchoring installation, characterized in having
 a block fixed to a lower anchoring installation, and 
 a pull down line connected to the buoyancy unit and guided through said block whereby in response to pulling down of said pull down line the buoyancy unit is pulled down to slacken the tether line to allow maintenance or replacement to be performed. 
 
     
     
       9. Device according to  claim 8  characterized in having a winch arrangement on an installation vessel and in having said pull down line installed and operated by said winch arrangement. 
     
     
       10. Device according to  claim 9  characterized in that said block includes a pulley unit. 
     
     
       11. Device according to  claim 10  characterized in having first preinstalled shackles adjacent the sea bed anchoring installation and second preinstalled shackles adjacent the buoyancy unit and in that said block is connect to said pre-installed shackles adjacent the sea bed anchoring installation, and said a pull down line end is connected to said preinstalled shackles adjacent the buoyancy unit. 
     
     
       12. Device according to  claim 8  characterized in that a tether line upper termination is arranged to connect to the buoyancy unit via a ROV operable interface component. 
     
     
       13. Device according to  claim 8  characterized in that a tether line lower termination is connected to the sea bed anchoring unit via an ROV operable interface component and includes a padeye unit for connection to a sea bed anchor.